microbiology

• Microbiologist


  A scientist who studies microscopic life forms and processes
• Microscopic organisms studied by microbiologists

  • Bacteria
  • Algae
  • Fungi
  • Some types of parasites and their vectors
• Microbiologists


  • Aim to solve a range of problems affecting our health, the environment, climate and food and agriculture
  • This can include the prevention, diagnosis and control of infections and disease, as well as ensuring that food is safe, understanding the role that microbes play in climate change, and developing green technologies
• 1. level course: Component 1.4
• Synoptic Links: Prokaryotic cell structure, Population growth curves
• Micro-organisms


  • Bacteria
  • Fungi
  • Protoctista
  • Viruses
• Bacteria and fungi


  Decay dead organisms, releasing and recycling nutrients
• Bacteria


  Some are pathogens and cause disease in humans, crops and domestic animals. Some have no effect and many are beneficial
• Bacteria reproduction


  Asexual, by binary fission, and can do so very rapidly
• The human body is made from one trillion cells but living in the gut are approximately one hundred trillion bacteria, made up of 500-1000 different species
• 140,000,000,000,000 = 1.4 x 10^14
• Bacteria


  • Size
  • Shape
  • Staining characteristics
  • Metabolic features
  • Antigenic features
  • Genetic features
• Archaea


  The smallest micro-organisms, some with a diameter of 0.4 µm
• E.coli


  Has a diameter of 1.8 µm and a length of 7 µm
• Calculating magnification


  1. M = I/A

  2. M = 49,000 um/2 um

  3. M = x24,500
• Bacterial shapes


  • Coccus (spherical) e.g. Staphylococcus, Streptococcus
  • Bacillus (rod-shaped) e.g. Escherichia coli
  • Spirillum (spiral/comma/corkscrew) e.g. Spirillum, Vibrio cholerae
• Bacterial grouping


  • Individual
  • Pairs
  • Chains
  • Clusters
• Bacterial metabolic features


  • Autotrophic
  • Phototrophic
• Autotrophic


  Synthesize all their cell constituents using carbon dioxide as the carbon source
• Phototrophic


  Photosynthesis with chlorophyll as e- donor, others use sulfur or hydrogen gas as an e- donor
• Bacteria can be distinguished from each other by their antigenic features
• Antigen


  A molecule that causes the immune system to produce antibodies against it
• The gram stain is used by microbiologists to distinguish between two types of bacteria; Gram positive and Gram negative
• Gram positive (+ve)


  Have a thick peptidoglycan cell wall, but no outer lipopolysaccharide membrane. They retain the initial crystal violet stain when washed with alcohol and appear purple under a microscope.
• Gram negative (-ve)


  Have a thin peptidoglycan cell wall and an outer lipopolysaccharide membrane. When washed with alcohol, they lose this outer layer with the crystal violet stain. Instead they take up the counter stain safranin and appear red under a microscope.
• Gram negative bacteria are not susceptible to some antibiotics such as penicillin, or lysozyme (in tears)
• Staphylococcus aureus are Gram positive bacteria


  Salmonella enterica are Gram negative bacteria
• Staphylococcus aureus


  Would appear purple because they retain the crystal violet stain
• Salmonella enterica


  Would appear red because they take up the red counter-stain safranin
• Staphylococcus aureus


  Would have a cell wall made from a thick layer of peptidoglycan
• Salmonella enterica


  Would have a thin layer of peptidoglycan with an outer lipopolysaccharide membrane
• Gram positive bacterial cell walls


  Take up and retain the crystal violet dye
• Gram negative bacterial cell walls

  Are treated with alcohol which removes the outer layer of lipopolysaccharide allowing safranin to stain the thin layer of peptidoglycan red
• Bacterial cell wall components

  • Peptidoglycan cell wall
  • Cell membrane
• Peptidoglycan cell wall


  Provides support to prevent osmotic pressure causing damage (lysis) to cell
• Cell membrane


  Selectively/partially/semi permeable membrane
• Gram stain results


  • Purple/violet
  • Remains colourless (crystal violet washed out)
  • Remains purple/violet (must be same colour)
  • Red/pink
• Binary fission


  Bacteria can undergo binary fission and reproduce quickly, given a suitable environment
• Conditions required for microbial growth

  • pH
  • Oxygen requirement
  • Temperature
  • Nutrients
• pH


  Most bacteria favour slightly alkaline conditions, whereas most fungi grow better in neutral to slightly acidic conditions